The present invention relates to backup power supplies and more particularly to the use of such with intermittently powered equipment.
Backup power supplies, sometimes called uninterruptable power supplies, are used to provide operational electrical power to equipment in times that the normal commercial or mains power system is not functioning. Backup power supplies generally comprise energy storage apparatus, such as batteries, connected to be charged from a mains power supply such as the 60 HZ, 120V power prevalent in the U.S. A power switching part of the backup power supply also connects the mains power directly to the equipment to be used. When a mains power failure occurs a conversion or invertor portion of the power supply is enabled to produce mains power e.g., 60 HZ, 120V from the stored power and the substitute power from the conversion portion is connected via the power switching part to the equipment to be powered. In this way the equipment can be powered during a mains power outage until the power stored by the backup power supply is used up or mains power is restored.
The power conversion apparatus of a backup power supply may consist of semiconductor switching circuitry connected to an input of a transformer. When the convertor is enabled due to mains power outage, an oscillator of predetermined frequency begins to drive the semiconductor switches to produce current pulses in the transformer. The equipment connected to the transformer output then has a continuing source of power for operation even though the mains power has stopped. The operations of the oscillator and semiconductor switches consume a significant amount of power from the power storage device whether or not the connected equipment requires power. Thus, the operation of the power converter is a backup power supply will consume significant stored power shortening the time that backup power is available, whether or not the equipment to be powered is actually taking power from the power supply. Such inefficiency is particularly problematic when the equipment to be powered is infrequently powered.
The use of backup power supply for example, with a barrier movement system, such as a garage door operator, provides advantages of barrier movement during power outage however, given the infrequent need for power the inefficiencies of the power convertor can needlessly shorten the period during which substitute power is available.
Additionally, backup power supplies frequently include protection circuitry which monitors the output power (current) of the supply and reduces the output power to prevent sustained overload. Such power reduction may involve reduction of output voltage or the elimination of one or more oscillator cycles to eliminate one or more current pulses to the output of the transformer. These steps at output power reduction may be responded to by the load as a power shutoff. When the equipment being powered includes an intelligent controller, such as a microprocessor, the controller may interpret the power reduction as a shut down and xe2x80x9cforgetxe2x80x9d action being performed. This could create a problem when the power supply is used with a barrier movement apparatus and a power reduction by the power supply is initiated by an increased power demand upon the barrier striking an unexpected obstruction. When power is again restored, after the controller has lost knowledge of its prior activity, the barrier could be moved in a manner harmful to the barrier or the obstruction.
In accordance with one aspect of the present invention a substitute power supply includes portions which are not enabled by a cessation of mains power until a user generated need for power is received.
In accordance with another aspect of the invention, when a controller of a barrier movement apparatus identifies that a power reduction by a substitute power supply was caused by the barrier striking an obstruction, the controller directs the opening of the barrier, away from the obstruction when power is returned.